Mark Cuban on ABC's "Shark Tank." "Shark Tank"/ABC Paul Graham, one of Silicon Valley's best-known investors and a cofounder of the startup accelerator program Y Combinator, doesn't seem to be a fan of ABC's hit show "Shark Tank."

Graham believes startups should focus on building great products, not on marketing, and for that reason he thinks shows like "Shark Tank" are a distracting waste of time for entrepreneurs.

He said as much on Twitter on Wednesday night, but billionaire investors Mark Cuban and Chris Sacca came back swinging.

Cuban, who owns the Dallas Mavericks, previously founded a company, Broadcast.com, that sold to Yahoo for over $5 billion in Yahoo stock. He is also one of the sharks, or judges, whom entrepreneurs pitch to on "Shark Tank."

He more or less called Graham and the startups his accelerator program had backed "entitled" and "arrogant."

Y Combinator is designed to help startups grow rapidly by providing guidance and money to founders in exchange for equity in their companies. YC has helped multibillion-dollar companies like Dropbox and Airbnb get off the ground.

But the companies that go through YC — which has a very low acceptance rate — are known for demanding a premium on their valuations when seeking funding from venture capitalists, hence Cuban's "entitled" jab.

But a lot of people feel accelerator programs aren't worth the equity founders give up to participate in them, which Cuban also pointed out to Graham.

Sacca is a billionaire angel investor who put early money into massive tech companies including Uber and Twitter. He has been a guest shark on ABC's show. He told Graham that pitching 7 million viewers every Friday night on ABC hardly seemed like a waste of time for a founder.